use super::info::text_value;
use super::types::{FLAG_HIDDEN, FLAG_NO_ROTATE, FLAG_NO_VIEW, Shape};
use super::{AnnotError, Dict, Document, ObjRef, Object, appearance};

// ── pages and /Annots ───────────────────────────────────────────────────────────────────────

/// The page object of each leaf page, in order.
pub fn page_refs(doc: &Document) -> Result<Vec<ObjRef>, AnnotError> {
    let root = doc.root().ok_or(AnnotError::NoPageTree)?;
    let pages = doc.get(root).as_dict().and_then(|d| d.reference(b"Pages")).ok_or(AnnotError::NoPageTree)?;
    Ok(PageWalk::new(doc, pages).collect())
}

/// Depth-first walk over the leaf pages under `top`. It keeps one cursor per open `/Kids` array,
/// never one entry per child, so a child listed many times or shared between nodes is skipped by
/// the seen check without being queued first (`pdfcraft_model::pages` walks the same way).
/// Cycles end at the seen check, a `/Kids` array object shared by several nodes is read once,
/// and at most a million nodes and four million `/Kids` entries are read.
pub(crate) struct PageWalk<'a> {
    doc: &'a Document,
    seen: std::collections::HashSet<ObjRef>,
    pub(crate) pending: Vec<(std::sync::Arc<Object>, usize)>,
    /// `/Kids` entries read so far.
    pub(crate) examined: usize,
}

impl<'a> PageWalk<'a> {
    pub(crate) fn new(doc: &'a Document, top: ObjRef) -> Self {
        let top = std::sync::Arc::new(Object::Array(vec![Object::Ref(top)]));
        Self { doc, seen: Default::default(), pending: vec![(top, 0)], examined: 0 }
    }
}

impl Iterator for PageWalk<'_> {
    type Item = ObjRef;

    fn next(&mut self) -> Option<ObjRef> {
        while let Some((kids, next)) = self.pending.last_mut() {
            let Some(kid) = kids.as_array().and_then(|a| a.get(*next)) else {
                self.pending.pop();
                continue;
            };
            let node = kid.as_ref();
            *next += 1;
            self.examined += 1;
            let Some(node) = node else { continue };
            if self.seen.len() >= 1_000_000 || self.examined > 4_000_000 {
                self.pending.clear();
                return None;
            }
            if !self.seen.insert(node) {
                continue;
            }
            let obj = self.doc.get(node);
            let Some(d) = obj.as_dict() else { continue };
            match d.get(b"Kids") {
                // A `/Kids` array object shared by several nodes is read under the first: under
                // the others it would only list nodes already seen.
                Some(Object::Ref(array)) if d.name(b"Type") != Some(b"Page") => {
                    if self.seen.insert(*array) {
                        self.pending.push((self.doc.get(*array), 0));
                    }
                }
                Some(kids) if d.name(b"Type") != Some(b"Page") => self.pending.push((self.doc.resolve(kids), 0)),
                _ => return Some(node),
            }
        }
        None
    }
}

pub(crate) fn page_ref(doc: &Document, page: usize) -> Result<ObjRef, AnnotError> {
    page_refs(doc)?.get(page).copied().ok_or(AnnotError::NoSuchPage(page))
}

/// The entries of a page's `/Annots` (references or inline dictionaries).
pub(crate) fn annots(doc: &Document, page: ObjRef) -> Vec<Object> {
    let obj = doc.get(page);
    let Some(a) = obj.as_dict().and_then(|d| d.get(b"Annots")) else { return Vec::new() };
    let list = doc.resolve(a).as_array().cloned().unwrap_or_default();
    #[cfg(test)]
    ANNOTS_ENTRIES_COPIED.with(|n| n.set(n.get() + list.len()));
    list
}

#[cfg(test)]
thread_local! {
    /// Entries copied out of pages' `/Annots` arrays.
    pub(crate) static ANNOTS_ENTRIES_COPIED: std::cell::Cell<usize> = const { std::cell::Cell::new(0) };
}

/// Replace a page's `/Annots`, writing into the shared array object when it is indirect. An empty
/// list removes a direct `/Annots`.
pub fn set_annots(doc: &mut Document, page: ObjRef, list: Vec<Object>) -> Result<(), pdfcraft_cos::CosError> {
    let existing = doc.get(page).as_dict().and_then(|d| d.reference(b"Annots"));
    match existing {
        Some(r) if doc.get(r).as_array().is_some() => doc.set(r, Object::Array(list)),
        _ => doc.update_dict(page, |d| {
            if list.is_empty() {
                d.remove(b"Annots");
            } else {
                d.set(b"Annots".to_vec(), Object::Array(list));
            }
        })?,
    }
    Ok(())
}

/// The annotation at `(page, index)` as an indirect object (inline dictionaries are promoted).
pub(crate) fn annot_ref(doc: &mut Document, page: usize, index: usize) -> Result<(ObjRef, ObjRef), AnnotError> {
    let p = page_ref(doc, page)?;
    let mut list = annots(doc, p);
    let entry = list.get(index).cloned().ok_or(AnnotError::NoSuchAnnotation { page, index })?;
    let r = match entry {
        Object::Ref(r) if doc.get(r).as_dict().is_some() => r,
        Object::Dict(d) => {
            let r = doc.add(Object::Dict(d));
            list[index] = Object::Ref(r);
            set_annots(doc, p, list)?;
            r
        }
        _ => return Err(AnnotError::NoSuchAnnotation { page, index }),
    };
    Ok((p, r))
}

pub(crate) fn annot_dict(doc: &Document, r: ObjRef) -> Dict {
    doc.get(r).as_dict().cloned().unwrap_or_default()
}

/// A Fill & Sign item: typed text, a check/cross/dot/line, or a typed, drawn or image signature.
///
/// New items carry `/PCFillSign`. Older files are recognised from the dictionaries PdfCraft
/// already writes (`/IT /FreeTextTypeWriter`, stamp `/Name`, drawn ink whose subject is
/// "Signature").
pub fn is_fill_sign(doc: &Document, d: &Dict) -> bool {
    if matches!(d.get(b"PCFillSign").map(|o| doc.resolve(o)).as_deref(), Some(Object::Bool(true))) {
        return true;
    }
    let subtype = d.name(b"Subtype").unwrap_or_default();
    if subtype == b"FreeText" && d.name(b"IT") == Some(b"FreeTextTypeWriter") {
        return true;
    }
    if subtype == b"Stamp" {
        if matches!(d.name(b"Name"), Some(b"PCCheck" | b"PCCross" | b"PCDot" | b"PCLine" | b"PCTypedSignature")) {
            return true;
        }
        if matches!(d.name(b"Name"), Some(b"PCCustomSignature" | b"PCCustomInitials"))
            && matches!(d.get(b"PCPictureImage").map(|o| doc.resolve(o)).as_deref(), Some(Object::Bool(true)))
        {
            return true;
        }
    }
    subtype == b"Ink" && text_value(doc, d, b"Subj").as_deref() == Some("Signature")
}

pub(crate) fn annotation_flags(doc: &Document, d: &Dict) -> i64 {
    d.get(b"F").and_then(|f| doc.resolve(f).as_int()).unwrap_or(0)
}

/// Whether the renderer keeps the annotation upright on a turned page: the NoRotate flag, with
/// `/F` read as the renderer reads it (a real truncated, a value that isn't a `u32` no flags).
pub(crate) fn drawn_upright(doc: &Document, d: &Dict) -> bool {
    let f = match d.get(b"F").map(|f| doc.resolve(f)).as_deref() {
        Some(Object::Int(i)) => *i,
        Some(Object::Real(r)) => *r as i64,
        _ => 0,
    };
    u32::try_from(f).is_ok_and(|f| i64::from(f) & FLAG_NO_ROTATE != 0)
}

/// Whether any page has a Fill & Sign annotation that flatten would bake in (not hidden).
pub fn has_visible_fill_sign(doc: &Document) -> bool {
    let Ok(pages) = page_refs(doc) else { return false };
    for page in pages {
        for entry in annots(doc, page) {
            let obj = doc.resolve(&entry);
            let Some(d) = obj.as_dict() else { continue };
            let flags = annotation_flags(doc, d);
            if flags & (FLAG_HIDDEN | FLAG_NO_VIEW) != 0 {
                continue;
            }
            if is_fill_sign(doc, d) {
                return true;
            }
        }
    }
    false
}

pub(crate) fn fill_sign_shape(shape: &Shape) -> bool {
    match shape {
        Shape::Typewriter { .. } | Shape::Mark { .. } | Shape::Signature { .. } | Shape::TypedSignature { .. } => true,
        Shape::CustomStamp { name, image: true, .. } => name == "Signature" || name == "Initials",
        _ => false,
    }
}

/// The embedded image of a Fill & Sign image signature or initials (0-based target).
/// Other stamps have appearances that can't be represented by this image alone.
pub fn signature_image(doc: &Document, page: usize, index: usize) -> Result<Option<ObjRef>, AnnotError> {
    let p = page_ref(doc, page)?;
    let list = annots(doc, p);
    let entry = list.get(index).ok_or(AnnotError::NoSuchAnnotation { page, index })?;
    let obj = doc.resolve(entry);
    let Some(d) = obj.as_dict() else { return Ok(None) };
    Ok((d.name(b"Subtype") == Some(b"Stamp")
        && matches!(d.name(b"Name"), Some(b"PCCustomSignature" | b"PCCustomInitials"))
        && matches!(d.get(b"PCPictureImage"), Some(Object::Bool(true))))
    .then(|| d.reference(b"PCPicture"))
    .flatten())
}

/// The page `/Rotate` the picture of the image signature at `(page, index)` is drawn turned back
/// by, so it reads upright on a page shown that way: 0 for one added to an unturned page, or by
/// another app. The picture appears turned by the page's current rotation less this.
pub fn picture_rotation(doc: &Document, page: usize, index: usize) -> Result<i64, AnnotError> {
    let p = page_ref(doc, page)?;
    let list = annots(doc, p);
    let entry = list.get(index).ok_or(AnnotError::NoSuchAnnotation { page, index })?;
    Ok(doc.resolve(entry).as_dict().map_or(0, appearance::picture_turn))
}

/// Leave page `page` of (a copy of) a document showing only its annotation at `index`, without
/// the page's content or other annotations, so a render draws that annotation alone: to lay it
/// over the page while it is dragged. `false`, with `doc` unchanged, when the annotation has no
/// normal appearance (`/AP /N`) for that render to draw.
pub fn isolate_annotation(doc: &mut Document, page: usize, index: usize) -> Result<bool, AnnotError> {
    let p = page_ref(doc, page)?;
    let entry = annots(doc, p).get(index).cloned().ok_or(AnnotError::NoSuchAnnotation { page, index })?;
    let has_normal = {
        let obj = doc.resolve(&entry);
        obj.as_dict().and_then(|d| d.get(b"AP")).is_some_and(|ap| doc.resolve(ap).as_dict().is_some_and(|ap| ap.contains(b"N")))
    };
    if !has_normal {
        return Ok(false);
    }
    set_annots(doc, p, vec![entry])?;
    doc.update_dict(p, |d| {
        d.remove(b"Contents");
    })?;
    Ok(true)
}